* Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote:
> On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote:
> >
> > * Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote:
> >
> > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > > index 357b32aaea48..5fdfe874229e 100644
> > > --- a/include/linux/rcupdate.h
> > > +++ b/include/linux/rcupdate.h
> > > @@ -1175,11 +1175,11 @@ do { \
> > > * if the UNLOCK and LOCK are executed by the same CPU or if the
> > > * UNLOCK and LOCK operate on the same lock variable.
> > > */
> > > -#ifdef CONFIG_PPC
> > > +#ifdef CONFIG_ARCH_WEAK_RELACQ
> > > #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for
> > > lock. */
> > > -#else /* #ifdef CONFIG_PPC */
> > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */
> > > #define smp_mb__after_unlock_lock() do { } while (0)
> > > -#endif /* #else #ifdef CONFIG_PPC */
> > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */
> > >
> > >
> >
> > So at the risk of sounding totally pedantic, why not structure it like the
> > existing smp_mb__before/after*() primitives in barrier.h?
> >
> > That allows asm-generic/barrier.h to pick up the definition - for example
> > in the
> > case of smp_acquire__after_ctrl_dep() we do:
> >
> > #ifndef smp_acquire__after_ctrl_dep
> > #define smp_acquire__after_ctrl_dep() smp_rmb()
> > #endif
> >
> > Which allows Tile to relax it:
> >
> > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep()
> > barrier()
> >
> > I.e. I'd move the API definition out of rcupdate.h and into barrier.h -
> > even
> > though tree-RCU is the only user of this barrier type.
>
> I wouldn't have any problem with that, however, some time back it was
> moved into RCU because (you guessed it!) RCU is the only user. ;-)
Indeed ...
[sounds of rummaging around in the Git tree]
I found this commit of yours from ancient history (more than a year ago!):
commit 12d560f4ea87030667438a169912380be00cea4b
Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Date: Tue Jul 14 18:35:23 2015 -0700
rcu,locking: Privatize smp_mb__after_unlock_lock()
RCU is the only thing that uses smp_mb__after_unlock_lock(), and is
likely the only thing that ever will use it, so this commit makes this
macro private to RCU.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: "linux-a...@vger.kernel.org" <linux-a...@vger.kernel.org>
So I concur and I'm fine with your patch - or with the status quo code as well.
Thanks,
Ingo
